1. Field of the Invention
This invention relates to a vehicle having a brake oil pressure controller. More particularly, it relates to a four-wheel-drive vehicle with an anti-locking brake system. Separate axles link each of the wheels to front and rear differentials. The differentials receive power from an engine. This invention further relates to a four-wheel-drive vehicle of the type wherein brake mechanisms for the front and the rear wheels have oil pressure modulators constructed so as to reduce braking oil pressure when the vehicle is in anti-locking operation, dependent upon the change in the oil pressure in the controlling chambers.
The present invention also relates to a four-wheel-drive vehicle with an anti-locking brake system, wherein a brake oil pressure unit which controls the oil pressure for different brakes at the front and rear wheels of the vehicle is provided with an anti-locking controller which reduces the oil pressure of the brakes when the wheels are about to be locked. The engine is directly coupled to either the front or rear axles. The other set of axles are coupled to the engine through a viscous coupling, which has a plurality of clutch disks spline-coupled to an input and an output, respectively. The clutch disks are placed together in a sealed oil chamber defined between the input and the output and rotate relative to each other. A clutch is disengaged when the anti-locking controller is in anti-locking operation.
2. Background Art
Four-wheel-drive vehicles have been developed in order to improve the mobility of the vehicle and its running performance on snowy roads or the like where there is a low coefficient of friction between the wheels and the road way. Attempts have been made to provide four-wheel-drive vehicles with an anti-locking brake system.
If an anti-locking brake system used for a conventional two-wheel-drive vehicle is applied to a four-wheel-drive vehicle as it is, the wheels of the four-wheel-drive vehicle interfere with each other so that sufficient anti-locking effect cannot be produced. When the front wheels of the four-wheel-drive vehicle are controlled by high selection and its rear wheels are controlled by low selection, it is likely that one front wheel is locked and the other front wheel rotates at a speed almost corresponding to the speed of the vehicle. It is also very likely that both the rear wheels rotate at a speed corresponding to about half of the speed of the vehicle and the rear wheels slip if they are directly coupled to the front wheels. In anti-locking control, the rotational speed of the front wheels is controlled to be relatively lower than that of the rear wheels in order to shorten the braking distance of the vehicle and enhance the stability of movement of the vehicle. However, if the front wheels are directly coupled to the rear wheels, the anti-locking control cannot be effected because the rotational speed of the front wheels is equal to that of the rear wheels.